Increased contact alignment tolerance for direct bonding

ABSTRACT

A bonded device structure including a first substrate having a first set of conductive contact structures, preferably connected to a device or circuit, and having a first non-metallic region adjacent to the contact structures on the first substrate, a second substrate having a second set of conductive contact structures, preferably connected to a device or circuit, and having a second non-metallic region adjacent to the contact structures on the second substrate, and a contact-bonded interface between the first and second set of contact structures formed by contact bonding of the first non-metallic region to the second non-metallic region. The contact structures include elongated contact features, such as individual lines or lines connected in a grid, that are non-parallel on the two substrates, making contact at intersections. Alignment tolerances are thus improved while minimizing dishing and parasitic capacitance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/269,412, filed Dec. 18, 2015, the entire contents ofwhich are incorporated by reference herein for all purposes.

BACKGROUND

Field

The field relates to direct wafer bonding, and more particularly to thebonding and electrical interconnection of substrates to be utilized insemiconductor device and integrated circuit fabrication.

Description of the Related Art

As the physical limits of conventional CMOS device are being approachedand the demands for high performance electronic systems are imminent,system-on-a chip (SOC) is becoming a natural solution of thesemiconductor industry. For system-on-a chip preparation, a variety offunctions are required on a chip. While silicon technology is themainstay technology for processing a large number devices, many of thedesired circuit and optoelectronic functions can now best be obtainedfrom individual devices and/or circuits fabricated in materials otherthan silicon. Hence, hybrid systems which integrate non-silicon baseddevices with silicon based devices offer the potential to provide uniqueSOC functions not available from pure silicon or pure non-silicondevices alone.

One method for heterogeneous device integration has been thehetero-epitaxial growth of dissimilar materials on silicon. To date,such hetero-epitaxial growth has realized a high density of defects inthe hetero-epitaxial grown films, largely due to the mismatches inlattice constants between the non-silicon films and the substrate.

Another approach to heterogeneous device integration has been waferbonding technology. However, wafer bonding of dissimilar materialshaving different thermal expansion coefficients at elevated temperatureintroduces thermal stresses that lead to dislocation generation,debonding, or cracking. Thus, low temperature bonding is desired. Lowtemperature bonding is also crucial for the bonding of dissimilarmaterials if the dissimilar materials include materials with lowdecomposition temperatures or temperature sensitive devices such as, forexample, an InP heterojunction bipolar transistor or a processed Sidevice with ultrashallow source and drain profiles.

The design of processes needed to produce different functions on thesame chip containing different materials is difficult and hard tooptimize. Indeed, many of the resultant SOC chips (especially those atlarger integration size) show a low yield. One approach has been tointerconnect fully processed ICs by wafer adhesive bonding and layertransfer. See, for example, Y. Hayashi, S. Wada, K. Kajiyana, K. Oyama,R. Koh, S Takahashi and T. Kunio, Symp. VLSI Tech. Dig. 95 (1990) andU.S. Pat. No. 5,563,084, the entire contents of both references areincorporated herein by reference. However, wafer adhesive bondingusually operates at elevated temperatures and suffers from thermalstress, out-gassing, bubble formation and instability of the adhesive,leading to reduced yield in the process and poor reliability over time.Moreover, the adhesive bond is usually not hermetic.

Wafer direct bonding is a technology that allows wafers to be bonded atroom temperature without using any adhesive. The room temperature directwafer bond is typically hermetic. It is not prone to introduce stressand inhomogeneity as in the adhesive bonding. Further, if the lowtemperature bonded wafer pairs can withstand a thinning process, whenone wafer of a bonded pair is thinned to a thickness less than therespective critical value for the specific materials combination, thegeneration of misfit dislocations in the layer and sliding or crackingof the bonded pairs during subsequent thermal processing steps can beavoided. See, for example, Q.-Y. Tong and U. Gosele, Semiconductor WaferBonding: Science and Technology, John Wiley & Sons, New York, (1999),the entire contents of which are incorporated herein by reference.

Moreover, wafer direct bonding and layer transfer is a VLSI (Very LargeScale Integration) compatible, highly flexible and manufacturabletechnology, and thus suitable for forming three-dimensional system-on-achip (3-D SOC). The 3-D SOC approach can be seen as the integration ofexisting integrated circuits to form a system on a chip.

Moreover, as the integration complexity grows, so do the demands on theintegration process to robustly unify diverse circuits at lowtemperature, preferably at room temperature, resulting in lower or noadditional stress and more reliable circuits.

Low or room temperature direct wafer bonding of metal between wafers ordies being bonded is desirable for 3D-SOC preparation. Such direct metalbonding can be used in conjunction with direct wafer bonding ofnon-metal between wafers or dies to result in electrical interconnectionbetween wafers or dies being bonded when they are mechanically bonded.Simultaneous metal and non-metal bonding can eliminate the need to forpost-bond processing, like substrate thinning, via etching, andinterconnect metallization, to achieve an electrical interconnectionbetween bonded wafers or die. Very small bonding metal pads can be used,resulting in very low parasitic impedance and resulting reduced powerand increased bandwidth capability.

Bonding of metals with clean surfaces is well-known phenomenon. Forexample, thermocompression wire bonding has been applied to wafer-levelbonding. Temperature, pressure and low hardness metals are typicallyemployed and usually results in residual stresses. See, for example, M.A. Schmidt, Proc. IEEE, Vol. 86, No. 8, 1575 (1998), Y. Li, R. W. Bower,I. Bencuya, Jpn. J. Appl. Phys. Vol. 37, L1068 (1988). Direct bonding ofPd metal layer covered silicon or III V compound wafers at 250-350° C.has been reported by B. Aspar, E. Jalaguier, A. Mas, C. Locatelli, O.Rayssac, H. Moricean, S. Pocas, A. Papon, J. Michasud and M. Bruel,Electon. Lett., 35, 12 (1999). However, Pd₂Si silicide or Pd-III Valloys, not metal Pd, are actually formed and bonded. Bonding of Au andAl at room temperature has been achieved by using ultrasonic andcompressive load at flip chip bonding, see, for example, M. Hizukuri, N.Watanabe and T. Asano, Jpn. J. Appl. Phys. Vol. 40, 3044 (2001). Roomtemperature metal bonding at wafer level has been realized in ultrahighvacuum (UHV) systems with a base pressure lower than 3×10⁻⁸ mbar.Usually an ion argon sputtering or fast atom-beam is used to clean thebonding surfaces followed by application of an external pressure to thebonding substrates. See, for example, T. Suga, Proc. The 2^(nd) Intl.Symposium on semiconductor wafer bonding, the Electrochemical Soc. Proc.Vol. 93-29, p. 71 (1993). Room temperature bonding between two Sisubstrates with thin sputtered Ti, Pt and Au films has also beenaccomplished using applied force after thin film sputter deposition at4-40 μbar of Ar pressure in a UHV system with base pressure less than3×10⁻⁸ mbar. See, for example, T. Shimatsu, R. H. Mollema, D. Monsma, E.G. Keim and J. C. Lodder, J. Vac. Sci. Technol. A 16(4), 2125 (1998).

Direct bonding of metal features or contacts and non-metal field regionsis disclosed in U.S. Pat. No. 7,485,968 and U.S. Pat. No. 6,962,835, thedisclosures of each of which are expressly incorporated by referenceherein. It can be challenging, however, to achieve both alignment ofmetal features from two substrates and achieve reliable metal bondingwhile also directly bonding surrounding non-metal regions.

SUMMARY

In one embodiment, a bonded structure is disclosed. The bonded structurecan include a first semiconductor element comprising a conductive firstcontact structure and a non-metallic first bonding region proximate thefirst contact structure, the first contact structure comprising aconductive first elongate contact feature. The bonded structure can alsoinclude a second semiconductor element comprising a conductive secondcontact structure and a non-metallic second bonding region proximate thesecond contact structure, the second contact structure comprising aconductive second contact feature. The first bonding region can be incontact with and directly bonded to the second bonding region. The firstelongate contact feature can be oriented non-parallel with and candirectly contact the second contact feature at an intersection betweenthe first elongate contact feature and the second contact feature.

In another embodiment, a bonding method is disclosed. The bonding methodcan include providing a first semiconductor element comprising aconductive first contact structure and a non-metallic first bondingregion proximate the first contact structure, the first contactstructure comprising a conductive first elongate contact feature. Themethod can include providing a second semiconductor element comprising aconductive second contact structure and a non-metallic second bondingregion proximate the second contact structure, the second contactstructure comprising a conductive second contact feature. The method caninclude orienting and bringing together the first and secondsemiconductor elements, such that the first elongate contact feature andthe second contact feature are nonparallel. The method can includedirectly bonding the first bonding region with the second bondingregion. The method can include directly bonding the first elongatecontact feature and the second contact feature at an intersectionbetween the first elongate contact feature and the second contactfeature.

In yet another embodiment, a bonded structure is disclosed. The bondedstructure can include a first semiconductor element comprising aconductive first contact structure and a non-metallic first bondingregion proximate the first contact structure, the first contactstructure comprising a conductive first grid pattern of multipleintersecting lines. The bonded structure can include a secondsemiconductor element comprising a conductive second contact structureand a non-metallic second bonding region proximate the second contactstructure, the second contact structure comprising a conductive secondgrid pattern of multiple intersecting lines. The first bonding regioncan be in contact with and directly bonded to the second bonding region.The first grid pattern can intersect and directly contact the secondgrid pattern.

In another embodiment, a bonded structure is disclosed. The bondedstructure can include a first semiconductor element comprising aconductive first contact structure and a non-metallic first bondingregion surrounding the first contact structure. The first contactstructure can include a conductive first elongate contact feature, thefirst elongate contact feature comprising a heavily doped semiconductormaterial. The first bonding region can comprise a lightly doped or anundoped semiconductor material. The bonded structure can include asecond semiconductor element comprising a conductive second contactstructure and a non-metallic second bonding region surrounding thesecond contact structure, the second contact structure comprising aconductive second contact feature. The first bonding region can be incontact with and directly bonded to the second bonding region. The firstelongate contact feature can directly contact and be directly bonded tothe second contact feature.

In yet another embodiment, a semiconductor element is disclosed. Thesemiconductor element can comprise a substrate comprising one or morelayers of non-metallic material. The semiconductor element can comprisea plurality of conductive traces embedded in the substrate, the tracesextending laterally through the substrate to route electrical signalslaterally. The semiconductor element can comprise an elongate contactfeature extending along and directly contacting a first trace of theplurality of traces, the contact feature exposed at a top surface of thesubstrate.

An object is thus to obtain mechanical and electrical contact betweenwafers and die with a single bonding step.

Another object is to provide a low or room temperature bonding method bywhich metallic bonding between wafers or die of semiconductor circuitscan be formed in ambient without using external pressure.

An additional object is to provide a low or room temperature bondingmethod by which metallic bonding of layers of any metal between wafersor die of semiconductor circuits can be formed at room temperature atwafer level in ambient without using external pressure by covering metallayers with a thin film of gold or copper or palladium.

Still another object is to provide a room temperature bonding method atwafer level in ambient without using external pressure by which metallicas well as covalent bonds are formed simultaneously at room temperatureon bonding surfaces of wafers or die comprised of semiconductor circuitswhere metal and other non-metal layers co-exist.

Another object is to provide a room temperature bonding method by whichdifferent substrates or different materials on different substrates withdifferent thermal expansion coefficients can be bonded together withoutgeneration of catastrophic stresses between the different substrates ordifferent materials on different substrates.

Still another object is a room temperature bonding method by which thebond strength between substrates approaches the mechanical fracturestrength of the substrates.

Another object is to provide a bonded device structure including devicesfabricated individually on separate substrates and bonded on a commonsubstrate.

A still further object is to provide a method and device whereby areliable mechanical bond can be formed at or near room temperature and areliable electrical contact can be subsequently formed with a simple lowtemperature anneal.

These and other objects are achieved by a bonded method and devicestructure including a first substrate having a first plurality ofmetallic bonding pads, preferably connected to a device or circuit, andhaving a first non-metallic region adjacent to the metallic bonding padson the first substrate, a second substrate having a second plurality ofmetallic bonding pads, preferably connected to a second device orcircuit, aligned or alignable with the first plurality of metallicbonding pads and having a second non-metallic region adjacent to themetallic bonding pads on the second substrate, and a contact-bondedinterface between the first and second set of metallic bonding pads.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosed embodiments and manyattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

FIG. 1A is a schematic depiction of a pair of unbonded substrates havingaligned metal bonding pads;

FIG. 1B is a schematic depiction of a pair of unbonded substrates havingthe aligned metal bonding pads contacted;

FIG. 1C is a schematic depiction of a pair of contacted substratesbonded in a non-metal region away from the metal bonding pads;

FIG. 1D is a schematic depiction of a pair of contacted substratesbonded across the non-metal regions except for a small unbonded ringarea near the metal bonding pads;

FIG. 2A is a schematic diagram illustrating bonding substrates withmultiple bonding pads prior to bonding;

FIG. 2B is a schematic diagram of bonding substrates after the bondingpads are contacted;

FIG. 2C is a schematic diagram of the bonding substrates asnonconductive regions are bonded;

FIG. 2D is graph showing the width of an unbonded ring area W as afunction of the metal pad thickness 2h separating the semiconductor diesas shown in the insert;

FIG. 3A is a schematic depiction of semiconductor die or wafer aftersurface planarization;

FIG. 3B is a schematic depiction of semiconductor die or wafer in whichsecond metal layer are formed and planarized with contact windows openedon metal pads;

FIG. 3C is a schematic depiction of second semiconductor die or waferwith a second metal layer.

FIG. 3D is a schematic depiction of an aligned metal bonding of two diesor wafers;

FIG. 4A is a schematic depiction of a part of a substrate showingimbedded metal pads in an oxide coating;

FIG. 4B is a schematic depiction of a pair of unbonded substrates havingreciprocal metal bonding pads;

FIG. 4C is a schematic depiction of a pair of bonded substrates showingthe reciprocal metal bonding pads contacted by the forces generated whenthe non-metal regions contacted and bonded;

FIG. 4D is a schematic depiction of a pair of smaller substrates bondedto a larger substrate;

FIG. 5A is a schematic diagram of an embodiment having a deformablematerial or void beneath the metal pad;

FIG. 5B is a schematic diagram of an embodiment having a deformablematerial beneath the metal pad;

FIG. 5C is a schematic diagram of two devices as shown in FIG. 5a bondedtogether.

FIG. 6A is a schematic diagram of an embodiment having reflowable metalmaterial exposed to the surface on two devices prior to direct waferbonding of the non-metal surfaces.

FIG. 6B is a schematic diagram of an embodiment having reflowable metalmaterial sealed by after direct wafer bonding of the non-metal surfaces.

FIG. 6C is a schematic diagram of an embodiment having reflowable metalreflowed after direct wafer bonding of non-metal surfaces sealed thereflowable metal.

FIG. 7A is a schematic diagram of an embodiment having reflowable metalmaterial exposed to the surface on two devices prior to direct waferbonding of the non-metal surfaces.

FIG. 7B is a schematic diagram of an embodiment having reflowable metalmaterial sealed by after direct wafer bonding of the non-metal surfaces.

FIG. 7C is a schematic diagram of an embodiment having reflowable metalreflowed after direct wafer bonding of non-metal surfaces sealed thereflowable metal.

FIG. 8A is a schematic side cross-sectional view of a firstsemiconductor element and a second semiconductor element before the twoelements are brought together.

FIG. 8B is a schematic side cross-sectional view of an intermediatebonded structure after the bonding regions are directly bonded together.

FIG. 8C is a schematic side cross-sectional view of a bonded structureafter the contact features are directly bonded together.

FIG. 9A is a schematic top plan view of the positions of conductivefeatures in a bonded semiconductor structure, according to oneembodiment.

FIG. 9B is a schematic side sectional view of the bonded semiconductorstructure of FIG. 9 a.

FIG. 10 is a schematic top plan view of the positions of conductivefeatures in a bonded semiconductor structure, according to anotherembodiment.

FIG. 11A is a schematic plan view of a first semiconductor elementhaving a plurality of elongate contact features connected withcorresponding underlying traces.

FIG. 11B is a schematic plan view of an exemplary contact feature andassociated underlying traces of the first semiconductor element, and acontact feature of a second semiconductor element aligned to makecontact in a crossing orientation with a contact feature of the firstsemiconductor element.

FIG. 11C is a schematic side cross-sectional view of two bondedsemiconductor elements including a direct connection between crossingcontact features of both elements.

FIG. 12A is a schematic top plan view of a conductive contact structurehaving a quadrilateral profile, according to various other embodiments.

FIG. 12B is a schematic top plan view of a polygonal conductive contactstructure having a quadrilateral profile, according to anotherembodiment.

FIG. 12C is a schematic top plan view of a conductive contact structurehaving a pentagonal profile, according to various embodiments.

FIG. 12D is a schematic top plan view of a conductive contact structurehaving a pentagonal profile, according to another embodiment.

FIG. 12E is a schematic top plan view of a conductive contact structurehaving a hexagonal profile, according to various embodiments.

FIG. 12F is a schematic top plan view of a conductive contact structurehaving a hexagonal profile, according to another embodiment.

FIG. 12G is a schematic top plan view of a conductive contact structurehaving a rounded profile, according to various embodiments.

FIG. 12H is a schematic top plan view of a conductive contact structurehaving a rounded profile, according to another embodiment.

DETAILED DESCRIPTION

Referring now to the drawings, wherein like reference numerals designatelike or corresponding parts throughout the several views, and moreparticularly to FIGS. 1A-1D and 2 illustrating a first embodiment of abonding process. In the first embodiment, direct metal-metal bonding isgenerated when metal contact regions on separate wafers upon alignmentare contact pressure bonded by the intrinsic forces generated whennon-metallic regions peripheral to the metallic regions undergoroom-temperature chemical bonding. Chemical bonding as used throughoutthis specification is defined as a bond strength developed when surfacebonds on the surface of one wafer react with the surface bonds on thesurface of an opposing wafer to form direct bonds across the surfaceelements, such as a covalent bond. Chemical bonds are manifest by theirhigh bond strengths, approaching for instance the fracture strength ofthe wafer materials, and thus are differentiated for example from mereVan der Waals bonding. Examples of chemical bond strengths achieved bythe methods of the disclosed embodiments are discussed below. In thechemical bonding process, substantial forces are developed. These forcescan be sufficiently great to increase the internal pressure of themetallic regions as the chemical bond propagates between the opposednon-metallic regions.

FIG. 1A shows two wafers 10, 13 with respective opposing wafer surfaces11, 14. The wafer surfaces may be pure elemental semiconductor surfaces,may be pure elemental semiconductor surfaces including a relativelysmall amount of native oxide, or may be an insulator such asoxide-coated surface. In various embodiments, the wafer surfaces maycomprise at least one of glass, silicon-on-insulator, silicon nitride,silicon carbide, sapphire, germanium, gallium arsenide, gallium nitride,polymers, indium phosphide, or any other suitable material. The surfacesmay be prepared as described in U.S. Pat. Nos. 6,984,571; 6,902,987; and6,500,694, the contents of each of which are hereby incorporated byreference in their entirety, to produce a smooth, activated surface.Techniques such as polishing or polishing and very slightly etching(VSE) may be used. A bonding layer may be deposited and polished orpolished and then slightly etched. The resulting surfaces arecomplementary and have chemical bonding surfaces that are planar andsmooth, having chemical bonding surface roughness in the range of 5-15Å, preferably no more than 10 Å, and more preferably no more than 5 Å.

Each wafer includes a set of metallic pads 12, 15 and a non-metallicregion adjacent to the metallic bonding pads in the surfaces 11, 14. Thenon-planarity and surface roughness of the metallic bonding pads may belarger than that of the chemical bonding surfaces. Pads 12, 15 may beelectrically connected, directly or indirectly, to internal circuitsand/or through silicon vias (TSVs), and may be used to route electricalconnections to the respective devices and/or circuits pre-fabricated onthe wafers. The pads are preferably formed before surface treatment, andVSE is preferably performed after the pads are formed. As shown in FIG.1A, pads 12, 15 are on the respective wafers are aligned. FIG. 1B showsthe wafers upon placing the wafers together to contact the respectivepads. At this stage, pads 12, 15 would be separable. In FIG. 1C, slightadditional pressure is applied to the wafers to elastically deform oneor both of the semiconductor wafers, resulting in contact between someof the non-metal areas on the wafers. The location shown of thecontacting is an example, and the contact may occur at differentlocations. Also, the contact may occur at more than one point. Thiscontact initiates chemical wafer-to-wafer bonding, and the bondedstructure is shown in FIG. 1D. The bonding seam 16 expands after theinitial chemical bonding to produce bonding seam 17 shown in FIG. 1D.The bond strength is initially weak and increases as the bondingpropagates, as explained in U.S. Pat. Nos. 6,984,571; 6,902,987; and6,500,694, which are incorporated by reference herein in their entirety.The opposing non-metallic regions are chemically bonded at room or lowtemperature.

In more detail, as the wafer surfaces including the metal bonding padscontact at room temperature, the contacting non-metal parts of opposingwafer surfaces began to form a bond at the contact point or points, andthe attractive bonding force between the wafers increases as the contactchemical bonding area increases. Without the presence of the metal pads,the wafers would bond across the entire wafer surface. The presence ofthe metal pads, while interrupting the bonding seam between the opposingwafers, does not prohibit chemical wafer to wafer bonding. Due to themalleability and ductility of the metal bonding pads, the pressuregenerated by the chemical wafer-to-wafer bonding in the non-metalregions may results in a force by which nonplanar and/or rough regionson the metal pads may be deformed resulting in improved planarity and/orroughness of the metal pads and intimate contact between the metal pads.The pressure generated by the chemical bonding is sufficient to obviateexternal pressure to be applied in order for these metal pads to beintimately contacted to each other. A strong metallic bond can be formedbetween the intimately contacted metal pads, even at room temperature,due to inter-diffusion or self-diffusion of metal atoms at the matinginterface. This diffusion is thermodynamically driven to reduce thesurface free energy and is enhanced for metals that typically have highinter-diffusion and/or self-diffusion coefficients. These high diffusioncoefficients are a result of a cohesive energy that is typically mostlydetermined by the mobile free electron gas that is not disturbed by themotion of metal ions during the diffusion. The wafer-to-wafer chemicalbonding in the non-metal regions thus effects electrical connectionbetween metal pads on the two different wafers. The geometrical andmechanical constraints governing this effect are described below.

An unbonded area around the bonding pad having a width W will begenerated in which the non-metal surfaces of the two wafers areprecluded from contacting (see FIG. 1D). As long as the thickness ofmetal films is not too large, the gaps between two bonding wafers ordies can be reduced, leaving a small unbonded area around each metalpad. This is illustrated in FIGS. 2A-2C, where wafer 20 with metal pads21 is ready to be bonded to wafer 22 with pads 23. A lateral gap 24 isbetween adjacent pads. The metal pads are contacted (FIG. 2B) and thewafers elastically deform to bond in the gaps 24 to form bonds 25 (FIG.2D). It is noted that the dimensions in FIGS. 2A-2C are not to scale.

The formula to calculate the width of the unbonded area as a function ofmetal film thickness, mechanical properties of the wafer or die, thewafer or die thickness, the bonding energy will be shown below. FIG. 2Dis a graph showing the relationship between the gap height 2h and thewidth w of an unbonded area. When the deformation of the wafers obeys anelastic constant given by Young's modulus E and the wafers each have athickness of t_(w), according to the simple theory of small deflectionof a thin plate, the width W of the unbonded area can be roughlyestimated by the following equation for W>2t_(w), where the metalbonding pads as a pair have a height of 2h above the wafer surface:

W=┌(2E′t _(w) ³)/(3γ)┐^(1/4) h ^(1/2)   (1)

where E′ is given by E/(1−v²) with v being Poisson's ratio.

It has been suggested that with decreasing h, the situation changesdrastically. See, for example, U. Goesele and Q.-Y. Tong, Proc. The2^(nd) Intl. Symposium on Semiconductor Wafer Bonding, theElectrochemical Soc. Proc. Vol. 93-29, p. 395 (1993). If W calculated byEq. (1) leads to values below W_(crit)=2t_(w), corresponding toh<h_(crit) where h_(crit)=5(t_(w)γ/E′)^(1/2), then an elastomechanicalinstability is supposed to occur, leading to an unbonded area with muchsmaller W that is independent of wafer thickness t_(w), and is given by:

W≈kh   (2)

where k is a dimensionless constant on the order of 1. Experimentally,as shown in FIG. 2D, if h<300 Å, W is much smaller than what ispredicted by Eq. (1). Further work by the inventors of the presentapplication has shown that, if the spacing between metal bonding padpairs 2R is smaller than 2W, the wafer pairs may not bond to each other.However, when 2R>2W, surfaces between the two unbonded areas around themetal posts will bond and the metal posts will be bonded andelectrically connected.

The pressure P on the metal bonding pairs that is generated by thebonding of the surrounding area can be expressed as:

P=(16E′t _(w) ³ h)/(3W ⁴)   (3)

Combining Eq. (3) with Eq. (1) or (2), when W>2 t_(w), the following isobtained:

P=8γ/3h,   (4)

and when W<2 t_(w), the following is obtained:

P=(16E′tw3)/(3k4h3)   (5)

For bonded silicon wafers where the metal pads have height h of 500 Åand the bonding energy is 300 mJ/m², the compressive pressure on themetal bonding pads is about 1.6×10⁸ dynes/cm², i.e., 160 atmospheres.Since this pressure is sufficiently high for metal bonding, there is noneed to apply any external pressure during bonding. When metal height his 300 Å or less, W<2t_(w) is satisfied and the pressure on the metalpairs is in the order of 5000 atmospheres if k=1 is assumed.

In one example, 5 mm diameter Au bonding pads with a thickness less than300 Å and a separation distance of 1 mm were deposited on oxide covered100 mm silicon wafers. Since the Au bonding pads were formed on thesurface of the oxide, they also had a height of 300 Angstroms above thesurface of the oxide. However, h can be much smaller than actual metalthickness because metal can be partially buried in oxide or otherinsulator and h is the height the metal extended above the die surface.A room temperature bonding technology has been developed that cleans andactivates the metal and the oxide surfaces compatibly andsimultaneously. The Au posts formed a metallic bond by room temperaturebonding at wafer level in ambient without using external pressure afterstorage in air for a period of time, e.g. 60 hr depending on the metalthickness and bonding energy. When the wafer pairs were forciblyseparated, by inserting a wedge between the bonded interface, either theAu or the Au/oxide layer peeled from the silicon substrate, indicatingthat the metal-to-metal bond formed was stronger than the adhesion ofthe Au pad on the oxide surface or the oxide on the silicon surface. Asmentioned above, a strong metallic bond can be formed between theintimately contacted metal pads at room temperature due tointer-diffusion or self-diffusion of metal atoms on the mating interfaceto reduce the surface free energy. The inter-diffusion or self-diffusioncoefficient between metal atoms increases exponentially withtemperature, in order to shorten the storage time to achieve fullmetallic bonding, annealing can be performed after room temperaturebonding. The preferred annealing time for metallic bonding between theAu posts shortened as the temperature increased. For this case, 5 hr waspreferred for 100° C., 1 hr for 150° C., and 5 min for 250° C. Thinnermetals can be bonded at lower temperatures than thicker metals due tohigher pressure generated by the bonding of non-metal surrounding areas.The time for the formation of metallic bonds at room temperature and atelevated temperatures becomes longer as the Au thickness (i.e., height)increases. For example, when the thickness of Au pads h is 600 Å, 5 minat 250° C. will form metallic bonds while at h=500 Å, 15 min at the sametemperature will form metallic bonds.

In flip-chip bonding of state-of-the art integrated circuits, the solderball pitch is about 1000 μm. Therefore, an unbonded area width aroundthe bonded metal posts that is comparable or less than 1000 μm issufficiently small for practical applications. Unbonded area widthssubstantially less than this amount can be obtained by this method. Forexample, experimental results show that when h=200 Å, W is 20 μm, andwhen h=300 Å, W is 30 μm. Because h is the height the metal extendedabove the die surface, h can be much smaller than actual metal thicknesssince metal can be partially buried in oxide or other insulator, h lessthan 200 Å can be readily achieved. In this case the unbonded ring widtharound the metal pads can be close to zero. The metal pad describedabove may be formed by processes such as, but not limited to,sputtering, evaporation, laser ablation, chemical vapor deposition, andother techniques know to those skilled in the art in which thicknesscontrol in the <100 Å range is typical.

FIGS. 3A-3C are schematic drawings of a process according to a secondembodiment, by which two different fully processed dies are bonded. Thedies are shown to have planar but uneven layer thickness, to demonstratethat the disclosed embodiments may be used in other instances other thaneven and planar layer thicknesses. In this process, as shown in FIG. 3A,a separate die 30 (only the oxide layer of die 30 is shown, forconvenience of explanation) has metal pads 31. The die may be a siliconwafer including semiconductor devices and circuits have opposingsurfaces of SiO₂. Surface 32 results after a CMP operation.

As shown in FIG. 3B, vias 36 have been formed and filled with metal toconnect with metal pads 31, metal interconnects 33 are formed on wafer30 to connect with the metal in vias 36, and a layer 34 of thickness t₂,of SiO₂ or other insulating material is formed on wafer 30. Portions 35of the SiO₂ layer having a width w₂ have been removed to expose metalpads 35. The surface of layer 34 is treated as described in U.S. Pat.Nos. 6,984,571; 6,902,987; and 6,500,694, including polishing orpolishing and slightly etching.

In FIG. 3C, a second wafer 37 has pads 38, vias 39 filled with metal,and interconnects 40 formed as shown. Interconnects 40 have a width w₁and a height t₁. Surface 41 of wafer 37 has been treated like surface32, as discussed above. The separate dies 30 and 37 are aligned andcontacted one to another to produce the bonded structure shown in FIG.3D. With the following relationships:

t ₁ =t ₂+δ₁ and w ₁ =w ₂+δ₂,

where t₁ and δ₁ are preferred to be the minimum thickness possible forthe deposition technology used, and δ₂ should be 2W corresponding to thecase of 2h=t₁. Compared with h=t₁ on both dies to be bonded, unbondedarea width W is significantly reduced. Thus interconnection between thepads on wafers 30 and 37 is made. If t₁ on both dies is less than thecritical thickness h_(crit) then layer 34 can be omitted.

During the initial contacting of the two wafers at room temperature, themetal pads are aligned, and the surfaces of the wafers conform to eachother by elastic deformation, when the gap due to the surface topographyof bonding wafers is sufficiently small and the bonding energy γ issufficiently high. Direct bonding occurs between the contacted materialsforming the metal interconnects between devices or circuits on adjoiningdies and between the wafer surfaces. The bond begins to form on contactand the bond strength increases, at room temperature, to form a metallicbond.

As in the first embodiment, wafer surfaces 32 and 41 including metalpads 33 and 40 contact, the contacting non-metal (e.g., semiconductor orinsulator) parts of opposing wafer surfaces 32 and 41 began to form abond at the contact points, and the bonding force increases as thecontact bonding area increases. Without the presence of protruding metalpads 33 and 40, the wafers would bond across the entire wafer surface.The presence of protruding metal pads 33 and 40, while interrupting thebonding seam between the opposing wafers, does not prohibit wafer towafer bonding. Rather, the pressure generated by the wafer-to-wafercontact in the non-metal regions translates into a force by which metalpads 33 and 40 are contacted even without any external pressure.

The method can be carried out in ambient conditions rather than beingrestricted to high or ultra-high vacuum (UHV) conditions. Consequently,the method is a low-cost, mass-production manufacturing technology. Thesize of metal films to be bonded is flexible and scalable to very smallgeometries because direct metallic bonding depends only oninter-molecular attraction force.

Direct metal bonding is preferable for better thermal management andpower capability of semiconductor devices. The direct metal bonding canreplace flip-chip bonding with much smaller bonding pads that arescalable. It is further possible that this metal bonding can be used torealize novel metal base devices (semiconductor-metal-semiconductordevices) see for example, T. Shimatsu, R. H. Mollema, D. Monsma, E. G.Keim and J. C. Lodder, IEEE Tran. Magnet. 33, 3495 (1997).

Further, the process is compatible with VLSI technology. The directmetal-to-metal bonding may be performed when wafers are fully processed.The direct metal-to-metal bonding also utilizes relatively low or roomtemperature bonding to minimize effects from the difference in thermalexpansion, since almost all metals have significantly higher thermalexpansion coefficients than semiconductor and insulators, such as thosenoted above (e.g., silicon or silicon dioxide).

The methods described herein can bond locally or across an entire wafersurface area. The methods, while not limited to the following examples,bond heterogeneous surfaces such that metal/metal, oxide/oxide,semiconductor/semiconductor, semiconductor/oxide, and/or metal/oxideregions can be bonded between two wafers at room temperature.

Numerous advantages are offered. For example, other methods of waferbonding and electrically interconnected constituent electrical contactsrequire thinning of bonded substrates, via etching and metal depositionafter wafer bonding. The methods described herein allow electricalinterconnections even without such post-bond process steps, allowing theelimination of mechanical damage caused by the die thinning.Furthermore, the elimination of deep via etching avoids step coverageproblems and allows the electrical connection to be scaled to smallerdimensions, resulting in an electrical interconnection with a smallerfootprint and reduced electrical parasitics between bonded wafers. Themethod is compatible with other standard semiconductor processes, and isVLSI compatible.

As such, the methods described herein are compatible with 3-D SOC(three-dimensional system-on-a chip) fabrication. This vertical metalbonding of metal pads or interconnects using plugs between bonded diessignificantly simplifies the SOC fabrication process and improves theSOC speed-power performance. The direct metal-to-metal bonding describedherein is scalable and can be applied to multi-die stacking SOC.

Besides generation of force sufficient to form metal-to-metalconnections, the methods facilitate low resistance metal bonding byoxide-free or nearly oxide-free surfaces of the metal bonding metalpads. For example, Au surface can be cleaned by ultraviolet/ozone andnitrogen plasma with no oxide left on the surfaces.

In another embodiment, the surfaces of the bonding metal pads(fabricated for example from metals such as Al or Cu) are coated withoxidation resistant metals, such as for example with gold (Au) orplatinum (Pt) layer. Since both Au and Pt are inert metals, no oxidewill be formed on the surfaces. To ensure that there is a minimum amountof oxide between Au or Pt and the host metal, sputter cleaning andevaporation deposition are employed, preferably immediately prior to thebonding process.

In a modification of the first embodiment, a thin metal overcoat layermay be formed on the metal pad and bonded as described above. Forexample, a layer as thin as 50 Å of an Au layer on an Al pad producedsuccessful metal pad bonding at room temperature. Therefore, metals suchas Au can be used as a bonding layer, enabling almost all metals to beutilized for direct bonding at room temperature by the foregoingmethods. When an insulator layer is deposed on a fully processed waferand contact openings are formed on the metal pads followed by a metaldeposition with thickness 100 Å more than the depth of the contactwindows, the metal pads now are extended above oxide layer only 100 Å,the pads can be separated each other by a very small distance, e.g. 20μm.

Besides Au or Pt, palladium (Pd) has been utilized in the direct bondingdescribed herein as an overcoat layer because Pd has good oxidationresistance. The surface diffusivity of Pd on Pd is very high resultingin a significant mass transport of Pd even at room temperature,especially given the contacting pressures exerted on the metal bondingpads by the bonding of the non-metal wafer surface regions. The nativeoxide between the two Pd bonding layers, if any, will be mechanicallydispersed allowing complete coverage with Pd of the physical interfacebetween the two contacted metal bonding pads.

In another modification of the first embodiment, a UV/ozone cleaningexposes the surfaces of the metal bonding pads to high ozoneconcentrations under a UV light to remove hydrocarbon contamination.Residual hydrocarbons on the surfaces of the metal bonding pads degrademetal bonding, and are nucleation sites for bubble formation between thebonding interfaces, resulting in out-gassing between the contactedsurfaces.

Experiments have shown that UV/ozone treatments can prevent interfacebubble formation. An HF dip of silicon wafers leads to hydrophobicsurfaces that are terminated mostly by H. The hydrophobic silicon wafersare treated with 4.77 g/m³ of ozone concentration combined with 1850 Åand 2540 Å UV irradiation from two 235 W UV lamps at room temperaturefor 15 min. followed by a second HF dip and bonding. The bonded pairs ofHF dipped hydrophobic silicon wafers generated no interface bubbles uponannealing from 300° C. to 700° C. for 15 hrs at each temperature clearlyindicating the effective removal of hydrocarbons from the wafersurfaces.

For Au and Pt, it is adequate to use UV/ozone cleaning before bondingwithout formation of metal oxide on the metal surfaces. For other metalsthat can be oxidized by ozone, a thin layer of Au on the metals canprevent oxidation, or the oxide can be removed by, for example,immersion in NH₄OH before bonding. In addition, plasma treatment withinert and/or nitrogen-containing gases, for example plasma treatments ina reactive ion etch mode (RIE) with gasses such as nitrogen and argon inthe plasma chamber, can clean metal surfaces and enhance the bondingenergy at room temperature for both metal/metal and oxide/oxide bonds.Further, an oxygen plasma can be used to remove contamination from thesurface of metals such as Au and Pt.

While numerous surface preparation treatments and metal/metal andoxide/oxide and semiconductor/semiconductor examples have beendescribed, other surfaces and preparation procedures could be used inwhich the corresponding metal, insulator, and semiconductor surfaces aresufficiently cleaned prior to contact such that the formation of roomtemperature bonding is not inhibited. In the case of Au protection or Aubonding, the process is metal and silicon dioxide compatible. After CMPand surface planarization and smoothing of the oxide surfaces, metalbonding pads are formed on bonding wafers as described above, a modifiedRCA 1 (H₂O:H₂O₂:NH₄OH=5:1:0.25), UV/ozone, and plasma treatment cleanthe surfaces of both metal and oxide without roughening the bondingsurfaces. A room temperature standard 29% NH₄OH dip removes particlesand oxide on the metal surfaces if any without degrading the silicondioxide surfaces. After spin-drying and room temperature bonding andstorage, strong covalent bonds and metallic bonds are formedspontaneously at bonding interfaces between oxide layers and betweenmetal surfaces, respectively. Besides the near planar bonding structuresshown in FIGS. 1A-1D, other structures can also utilize the principlesdescribed herein. For example, a second embodiment is shown in FIGS.4A-4C, where wafers including metal via interconnections are bonded to asmaller die. FIG. 4A depicts a magnified view of a substrate 50including metal interconnects 51. In FIG. 4A, the metal interconnectsare embedded in a silicon dioxide layer 52 such as a PECVD oxide,thermal oxide, or spin-on glass. Interconnects 51 extend above the layer52 to a height as discussed previously. FIG. 4A also shows smaller die53 having metal contact 54 and silicon dioxide layer 55.

Following forming an insulating layer 58 on both dies of a material suchas silicon dioxide, a standard via etch and metal fill, followed bychemical mechanical polish and surface treatment are used to prepare thelayers 58 for bonding. FIG. 4B depicts a pair of opposing wafers withreciprocal metal bonding pads 56 and 57. FIG. 4C shows the contactingand subsequent bonding of these two opposing substrates, forming bond59.

Here, as before, the bonding of the non-metal regions generates therequisite forces to form the metal-to-metal interconnections across thedies. As depicted in FIG. 4C, the bonding of the oxide layers generatesthe requisite bonding force for direct metal-to-metal contact of themetal bonding pads 56 and 57. A plurality of dies 53 may be prepared andbonded to die 60, as shown in FIG. 4D.

In the metal-to-metal direct bonding of the first and secondembodiments, the thickness of bonding metal films extended above diesurface is preferably thin to minimize the unbonded ring area around themetal posts. Further, the thickness of bonding metal pads is scaleable,and VLSI compatible size metal posts or pads can be made and bonded.When the metal film thickness is below a certain value, the width of theunbonded ring area is significantly reduced so that the spacing betweenmetal posts permits small spacing (e.g. <10 μm) between the metalbonding pads to be used.

A third embodiment allows a significant increase in the metal heightabove the non-metal surface and/or significant reduction in non-bondedarea near the metal while maintaining an acceptable electricalconnection between metal portions formed on separate wafers. In thisembodiment, deformation of material in the vicinity of the metalmaterial that forms the electrical contact is designed to result fromthe pressure at the metal surfaces from the wafer-to-wafer chemicalbonding of the non-metal portions. This deformation may result in lesspressure applied to the metal after the bonding process is complete, butadequate pressure to form an acceptable electrical connection betweenthe metal portions. This deformation allows the gap near the metalsurfaces to be significantly reduced or eliminated.

The object of the deformable material in the vicinity of the metalmaterial forming the electrical contact is to allow the pressuregenerated by the chemical bonding of the non-metal surfaces to besufficient to recess the metal material sufficiently into its respectivesurface so that the gap near the metal surface can be significantlyreduced or eliminated. In general, the deformable material is comprisedof non-metal portions because the pressure generated by thewafer-to-wafer chemical bonding is typically about one part in 10,000 or1% of 1% of that required to deform typical metals. The recess of themetal into its respective surface allows the starting height of themetal surface above the non-metal surface to be substantially higherthan after the recess. This significantly increases the tolerances ofthe metal surface required to prepare the wafers for bonding andsubsequently the manufacturability of the embodiment. The deformationalso substantially reduces or eliminates the non-bonded region aroundthe metal allowing a substantial increase in the number of connectionsthat can be made in a given area and increasing the bond strength of thebonded and interconnected parts.

The deformation can be facilitated by the inclusion of a non-metalregion underneath the metal surface, as illustrated in FIG. 5A. A diewith a substrate 55 has a metal pad 50 formed on a layer 51 that is tobe bonded to a corresponding layer on another device. Region 53, filledwith a deformable non-metal material such as a low K dielectricmaterial, is formed in layer 52 by standard photolithography, etchingand deposition techniques. Layer 52 and region 53 are formed on layer54. Any number of layers may be formed on substrate 54. Also, region 53may be much larger or layer 52 may be formed of the low K material, asshown in FIG. 5B.

Region 53 may also be a void containing a vacuum or compressible gaslike air, or it may be a compressible non-gas solid material with asufficiently low compressibility that the pressure generated by thebonding will deform the metal into the region. The void may be formed ina manner similar to that used to fabricate metallic air bridges commonin compound semiconductor integrated circuit fabrication. One example ofthis fabrication is as follows: 1) etch a recess in a planar, non-metalsurface, 2) fill the recess with a removable material like photoresistsuch that the removable material is in the recess, but not outside therecess. This may, for example, be done by conventional spin coating ofphotoresist, resulting in a thicker photoresist in the recess thanoutside the recess, followed by blanket (non-patterned) etching of thephotoresist of an amount sufficient to remove the material outside therecess but not sufficient to remove the material in the recess, 3)patterning a metal feature that transverses the recess but does notentirely cover the recess, leaving an exposed portion of the recess, and4) removal of the removal material in the recess by accessing theexposed portion of the recess. An example of a compressible non-gassolid material is a low K dielectric used in semiconductormanufacturing. The depth of this region is typically comparable to orgreater than the desired height of metal above the non-metal surface.Another die to which the die of FIG. 5A is to be bonded may also have aregion such as region 53 in a corresponding position beneath a metal padto be bonded to pad 50. This is illustrated in FIG. 5C, where it isnoted that FIG. 5C is a schematic drawing and is not shown to scale.Here, pads 50 and 56 are bonded by the compressive force generated bybonding of layers 51 and 57. The upper die in FIG. 5C includes asubstrate 61 with pad 56 formed over void or low K material region 59 inlayer 58. Layer 58 is formed on layer 59. Again, the upper die may havemany layers.

In this embodiment, when the wafers are bonded, the metal surfaces arecontacted and deformation with respect to each other occurs during thechemical bonding process. The deformation relieves some of the pressureapplied by the bonding process, but sufficient pressure remains tomaintain the metal surfaces in contact and maintain an acceptableminimum contact resistance between the two metal surfaces on the twoseparate wafers. As the metal deforms into the region under the metal,the bonding surfaces are allowed to come into contact in a lateralannulus very close or immediately adjacent to the metal, resulting in amaximum bonding area between the non-metal surfaces. A minimumchemically-non-bonded region of 1-10 microns, or less, adjacent to themetal contact, can thus be formed by the disclosed embodiments.

The deformable region is designed to have a minimum width to maximizethe number of possible electrical interconnections. The deformableregion width primarily depends on the metal thickness and the metalheight above the non-metal surface. These parameters are approximatelydetermined by the following relations.

Stress=(2/3)*(Young's Modulus of Metal)(1/1−Metal Poisson'sRatio)*(metal height above surface/half width of region)²

and

Pressure=Stress*4*metal thickness*metal height above surface/(half widthof region)²

Where the pressure is that generated by the bonding process. A referencefor these relations can be found in the “Handbook of Thin FilmTechnology”, Maissel and Glang, 1983 Reissue, pp. 12-24.

For example, for a metal thickness of about 0.1 micron and a metalheight above the region of about 0.1 micron above the surface and aregion width of about 1 micron, the pressure generated during bonding isapproximately sufficient to deform the metal into the region (assumingcompressibility of the region can be neglected). Note that this 0.1micron metal height would have resulted in an unbonded annulus or ringwidth around the metal of about 1 mm if the metal was not deformable.The manufacturability is thus increased substantially by requiring lesscontrol of the metal height above the non-metal surface. Furthermore,the non-bonded area is substantially decreased allowing a significantincrease in the number of metal to metal contacts that can be made andresulting in an increase in the chemical bonding energy. If thecompressibility of the region cannot be neglected, then the thickness ofthe metal should be reduced accordingly and/or the metal height abovethe non-metal surface should be reduced accordingly and/or the width ofthe region should be increased accordingly. Note that the percentageamount the width of the region should be increased is less than thepercentage amount the metal height above the non-metal surface, or themetal thickness, should be reduced.

A fourth embodiment further relaxes the mechanical design constraints inthe vicinity of the metal contacts described in the first, second, andthird embodiments by relying on a low temperature, post-bond reflowanneal to form reliable electrical interconnections between chemicallybonded wafers. A description of this embodiment is provided withreference to FIGS. 6A-C and 7A-C.

FIG. 6A shows substrates 60 and 61 with planar surfaces. Recesses 62 and63 are formed in substrates 60 and 61, respectively, and metal pads 64and 65 are formed in recessed 62 and 63 respectively. The planarsurfaces are suitable for chemical bonding as described previously. Themetal or combination of metals making up pads 64 and 65 can reflow atlow temperatures. Examples of such a metal is indium that reflows at amelting temperature of 160 degrees C., and such a combination of metalsis 96.5% tin and 3.5% silver that reflows at a eutectic meltingtemperature of 220 degrees C.

After the surfaces in FIG. 6A are prepared for direct chemical bondingand the surfaces are placed together, a chemical bond is formed betweenthe planar surfaces. Compared to embodiments 1 and 2, there is no gapnear the metal contacts because the contacts are recessed, although areliable electrical interconnection is not yet made.

After the chemical bond in FIG. 6B has been formed, a void 66 is formedby partially metal-filled recesses from both wafers. This void does notimpede the wafer surfaces from coming together and forming a chemicalbond like the metal contacts do in the first and second embodiments. Amaximum bond area is thus realized that maximizes the bond energy. Afterthis high bond energy chemical bond has been formed, a low temperaturereflow anneal reflows the metal in the recesses resulting in wetting ofthe metal from the opposing wafers together and resulting in aninterconnected metal structure with high reliability. Portions 67 areformed by the reflow to connect pads 64 and 65. This reflow is assistedwith a combination of capillary action for recesses with high aspectratios and gravity as, for example, if the wafers are rotated during theanneal.

In a fifth embodiment, similar to the fourth embodiment, one of thesurfaces in FIG. 6A has the metal recesses replaced with metal plateaus,such that the height of the metal plateau above the planar surface onone wafers is less than the depth of the metal recess below the planarsurface on the other wafers as shown in FIG. 7A. Substrates 70 and 71have respective metal pads 72 and 73. Pads 72 are formed in recesses 74.In this case, the metal surfaces do not, in general, touch after theplanar surfaces forming a chemical bond are placed in contact as shownin FIG. 7B. The surfaces of substrates 70 and 71 are prepared for directchemical bonding and the surfaces are placed together as in the aboveexample, and a chemical bond is formed between the planar surfaces (FIG.7B). After reflow, the metal on the two different wafers is wettedtogether, forming portions 75, in a manner similar to FIG. 6C, resultingin FIG. 7C.

Hence, the embodiments described herein offer numerous advantages anddistinctions from prior low temperature wafer bonding techniques. Themetal to metal direct bonding is spontaneous and requires no externalforces at room temperature. The pressure applied on the metal posts thatis required for metal-to-metal bonding is generated by bonding processitself, and not external forces. The metal-to-metal direct bondingdescribed above can be performed under ambient conditions and thefollowing are realized: wafer level or die size bonds, strong metallicAu—Au, Cu—Cu or metal-to-metal bonds formed at room temperature, andstrong metallic bond of metals other than Au and Cu can be formed atroom temperature by covering the metals with a ˜50 Å Au layer. Thus,simultaneous bonding of metal/metal, oxide/oxide and metal/oxide can beachieved. The metal-to-metal direct bonding is compatible with standardVLSI processing and therefore, is a manufacturable technology. The metalto metal direct bonding is compatible with bonding of materials coveredwith silicon oxides, silicon, or silicon nitride. In variousembodiments, the metal to metal direct bonding is compatible withbonding of materials covered with at least one of glass,silicon-on-insulator, silicon carbide, sapphire, germanium, galliumarsenide, gallium nitride, polymers, indium phosphide, or any othersuitable material.

Facilitating the metal-to-metal direct bonding is the direct bonding ofthe non-metal regions proximate to the metal bonding pads. As previouslydiscussed, it is the direct bonding in these regions that generates theresultant force on the opposing metal bonding pads. The direct bondingof the non-metallic regions covalently bonds in air silicon dioxide orother insulator covered wafers, e.g., wafers covered with at least oneof glass, silicon-on-insulator, silicon carbide, sapphire, germanium,gallium arsenide, gallium nitride, polymers, indium phosphide, or anyother suitable material. Other materials can be utilized, for example,fluorinated oxide surface layers that may also be dipped in an ammoniasolution prior to bonding. More generically, any material with an openstructure surface that can be terminated by OH, NH or FH groups, andporous low k materials when brought into contact at room temperature canform a covalent bond.

Silicon dioxide formed by any method such as deposition, thermally orchemically oxidation, and spin-on glass, can be used in pure or dopedstates.

Applications include but are not limited to vertical integration ofprocessed integrated circuits for 3-D SOC, micro-pad packaging, low-costand high-performance replacement of flip chip bonding, wafer scalepackaging, thermal management and unique device structures such as metalbase devices.

FIG. 8A is a schematic side cross-sectional view of a firstsemiconductor element 101 a and a second semiconductor element 101 bbefore the two elements 101 a, 101 b are brought together. Thesemiconductor elements 101 a, 101 b can comprise correspondingnon-metallic bonding regions 106 a, 106 b and conductive contactstructures 102 having contact features 103 a, 103 b. As shown in FIG.8A, the contact features 103 a, 103 b can be disposed below the bondingsurfaces 106 a, 106 b such that corresponding recesses 115 a, 115 b areformed in the semiconductor elements 101 a, 101 b. The contact features103 a, 103 b can be formed in the recesses 115 a, 115 b in any suitablemanner. For example, in some embodiments, the recessed contact features103 a, 103 b can be formed using a damascene process. In such damasceneprocesses, one or more trenches can be formed in the semiconductorelement 101 (e.g., by etching), and conductive material can be suppliedin the trenches. The conductive material over field regions can bepolished or otherwise removed to as to form the recessed contactfeatures 103 a, 103 b of FIG. 8A.

The contact features 103 a, 103 b can comprise any conductive materialssuitable for the embodiment of FIGS. 9A-9B described below. The bondingregions 106 a, 106 b and contact features 103 a, 103 b can comprise anymaterials suitable for use with the embodiment of FIGS. 9A-9B describedbelow. As explained below, the bonding regions 106 a, 106 b can beprepared for direct bonding. For example, as explained with respect tothe embodiment of FIGS. 9A-9B, the bonding regions 106 a, 106 b can bepolished, very slightly etched, and/or terminated with a desired species(such as nitrogen). Moreover, as shown in FIG. 8A, interconnects 105(e.g., TSVs) can connect the contact feature 103 b to the exterior ofthe semiconductor element 101 b to provide electrical communication tothe larger electrical system. Furthermore, although not shown, there maybe additional layers of internal metallization between the interconnects105 and the contact feature 103 a. The metallization and/orinterconnects 105 can be formed before or after bonding the two elements101 a, 101 b together. Additional details may be found at least in U.S.Pat. No. 7,485,968, which is incorporated by reference herein in itsentirety and for all purposes.

FIG. 8B is a schematic side cross-sectional view of an intermediatebonded structure 100′ after the bonding regions 106 a, 106 b aredirectly bonded together. When the bonding regions 106 a, 106 b arebrought into contact, the bonding regions 106 a, 106 b can be directlybonded together so as to form a chemical bond (e.g., a covalent bond)without an intervening adhesive. As explained above, the direct bondingcan be conducted at room temperature and/or without the application ofexternal pressure. After the bonding regions 106 a, 106 b are directlybonded together, there may remain an initial gap 120 between thecorresponding contact features 103 a, 103 b. It will be understood thatsuch a gap 120 can also be achieved after contacting the bonding regions106 a, 106 b even if the contacts on one side protrude, as shown in FIG.7B.

FIG. 8C is a schematic side cross-sectional view of a bonded structure100 after the contact features 103 a, 103 b are directly bondedtogether. In various embodiments, for example, the semiconductorelements 101 a, 101 b can be heated after directly bonding thenonconductive bonding regions 106 a, 106 b. In various embodiments, thesemiconductor elements 101 a, 101 b can be heated in a range of 75° C.to 350° C., or more particularly, in a range of 100° C. to 250° C.Heating the semiconductor elements 101 a, 101 b can increase theinternal pressure of the contact features 103 a, 103 b and can causethem to expand to fill the gap 120. Thus, after the contacts features103 a, 103 b are directly bonded together, the contact 125 cansubstantially fill the void between the two semiconductor elements 101a, 101 b.

As shown in FIG. 8C, the first bonding region 106 a can be directlybonded to the second bonding region 106 b along an interface 130. Theinterface 130 between the first bonding region 106 a and the secondbonding region 106 b can extend substantially to the first and secondcontact features 103 a, 103 b, i.e., to the directly bonded contact 125.Thus, as shown in FIG. 8C, after the contact features 103 a, 103 b arebonded together, there may be no gap between the contact feature 103 a,103 b and the proximate bonding regions 106 a, 106 b. Unlike theembodiments of FIGS. 1A-5C, the elements may exhibit no plasticdeformation surrounding the contacts 125.

The distance below the bonding regions 106 a, 106 b of the semiconductorelements 101 a, 101 b can be less than 20 nm and preferably less than 10nm. Bonding followed by temperature increase may increase the internalpressure between contact features 103 a, 103 b as described above andcan result in improved metal bonding, metal contact, metal interconnect,or conductance between contact structures 102. The slight distance ofcontact features 103 a, 103 b below the respective bonding regions 106a, 106 b can be an average distance over the extent of the contactstructures 102. The topography of the contact structures 102 may alsoinclude locations equal, above, and below the average distance. Thetotal height variation of the contact structures 102, given by thedifference between the maximum and minimum height, may be substantiallygreater than the root-mean-square (RMS) variation. For example, acontact structure with a RMS of 1 nm may have a total height variationof 10 nm.

Accordingly, although contact features 103 a, 103 b may be slightlybelow the bonding regions 106 a, 106 b, a portion of contact features103 a, 103 b may extend above the bonding regions 106 a, 106 b,resulting in a mechanical connection between the contact features 103 a,103 b after bonding of the non-metal bonding region 106 a to non-metalbonding region 106 b. This mechanical connection may not result in anadequate electrical connection between contact features 103 a, 103 b dueto an incomplete mechanical connection or native oxide or othercontamination on contact features 103 a, 103 b. Subsequent temperatureincrease may improve the metal bonding, metal contact, metalinterconnect, and/or conductance between contact features 103 a, 103 bas described above.

Alternatively, the temperature increase may result in mechanical contactand/or desired electrical interconnection between contact features 103a, 103 b if the highest portion of contact features 103 a, 103 b isbelow bonding regions 106 a, 106 b and there is not a mechanical contactbetween contact features 103 a, 103 b after bonding.

Alternatively, contact features 103 a may be below the surface ofbonding region 106 a and contact features 103 b may be above bondingregion 106 b, or contact features 103 a may be above the surface ofbonding region 106 a and contact features 103 b may be below the surfaceof bonding region 106 b. The difference between the distances of contactfeatures 103 a, 103 b below bonding regions 106 a, 106 b (or vice versa)can be slightly positive. Alternatively, the difference between thedistances of contact features 103 a, 103 b below bonding regions 106 a,106 b can be nominally zero or slightly negative and a post-bondtemperature increase may improve the metal bonding, metal contact, metalinterconnect, conductance between contact features 103 a, 103 b asdescribed above.

The height or depth of contact features 103 a, 103 b relative to thebonding regions 106 a, 106 b of elements 101 a, 101 b can be controlledwith a polishing process that forms the surfaces of elements 101 a, 101b, for example using chemical mechanical polishing (CMP). The CMPprocess typically may have a number of process variables including butnot limited to the type of polishing slurry, rate of slurry addition,polishing pad, polishing pad rotation rate, and polish pressure. The CMPprocess can be further dependent on the specific non-metal and metalmaterials comprising the semiconductor elements 101 a, 101 b, relativepolishing rates of non-metal and metal materials (similar polishingrates are preferred, for example nickel and silicon oxide), size, pitchand grain structure of the contact features 103 a, 103 b, andnon-planarity of bonding regions 106 a, 106 b. Alternate polishingtechniques, for example slurry-less polishing, may also be used.

The height or depth of contact features 103 a, 103 b relative to thebonding regions 106 a, 106 b may also be controlled with a slight dryetch of the material around contact features 103 a, 103 b on thesurfaces of semiconductor elements 101 a, 101 b, for example using aplasma or reactive ion etch using a mixture of CF₄ and O₂, for thesurfaces comprised of certain dielectric materials, for example siliconoxide, silicon nitride, or silicon oxynitride, preferably such that anincrease in surface roughness, that would significantly decrease thebond energy between said surfaces, results. Alternatively, the height ofcontact features 103 a, 103 b may be controlled by the formation of avery thin metal layer on the contact features 103 a, 103 b. For example,electroless plating of some metals, for example gold, can beself-limiting to a very thin layer, for example approximately 5-50 nm.This method may have the additional advantage of terminating anoxidizing metal with very thin non-oxidizing metal, for example gold onnickel, to facilitate the formation of electrical connections.

Thus, in the bonding sequence, for embodiments such as those of FIGS.1A-5C, contact between contact structures from opposing substrates canprecede or be simultaneous with contact between bonding regions ofopposing substrates. For embodiments such as those of FIGS. 6A to 8C,contact between contact structures from opposing substrates can occurafter contact between bonding regions of opposing substrates.

Examples of Elongate Contact Features

In some arrangements, it may be challenging to align the contact pads ofone semiconductor element with the corresponding contact pads of anothersemiconductor element. Some contact pads (such as the metallic pads 12,15 of FIGS. 1A-1D) may have a relatively small or compact size andshape, which can make it difficult for traditional pick-and-place toolsto align corresponding contact pads. For example, many pick-and-placetools have an alignment capability in a range of 2 microns to 10microns, or in a range of 5 microns to 10 microns. Contact pads havingmajor dimensions outside or near these ranges may be difficult to alignusing traditional pick-and-place tools, and may entail more expensivealignment equipment and/or procedures.

In some arrangements, the overall size of the contact pad may beincreased so as to improve the alignment of corresponding pads from twobonded semiconductor elements. However, increasing the size of thecontact pads may take up valuable real estate on the semiconductorelements. Moreover, increasing the size of the contact pads may alsoincrease parasitic capacitance, thereby increasing power consumptionand/or reducing the bandwidth of the semiconductor elements. Inaddition, larger contact pads may also increase the effect of dishing onpolished surfaces of the respective semiconductor elements. Theresulting large dishing effect may cause the non-conductive bondingand/or conductive regions to bond in a non-uniform manner. For directbonding of metal (or conductively-doped semiconductor) and non-metalregions as described herein, the height of contacts above or depth ofcontacts below the substrate surface can be critical to achieving thedesired contact bonds.

Accordingly, there remains a continuing need to provide improvedalignment accuracy between corresponding contact pads while maintainingrelatively small feature sizes during bonding. In various embodimentsdisclosed herein, a first semiconductor element can comprise aconductive first contact structure and a non-metallic first bondingregion proximate the first contact structure. The first contactstructure can include a conductive first elongate contact feature. Asecond semiconductor element can comprise a conductive second contactstructure and a non-metallic second bonding region proximate the secondcontact structure. The second contact structure can include a conductivesecond contact feature. The first bonding region can be in contact withand directly bonded to the second bonding region. The first elongatecontact feature can be oriented non-parallel with and can directlycontact the second contact feature at an intersection between the firstelongate contact feature and the second contact feature. The secondcontact feature can also be an elongate contact feature.

Because at least one of the contact features is elongated, greatermisalignments can be tolerated when the two semiconductor elements arebrought together. Furthermore, the use of an elongate contact featurecan enable the use of relatively small feature sizes, such as relativelynarrow lines relative to the larger contact regions. For example, eventhough the contact feature may be much longer along its length than itswidth in order to facilitate alignment, the relatively thin width of theelongate contact feature significantly reduces contact height or depthvariations due to dishing during polishing. Furthermore, the narrowfeature width facilitates a relatively small parasitic capacitance and arelatively low footprint on the element.

FIG. 9A is a schematic top plan view of a bonded semiconductor structure100, according to one embodiment. FIG. 9B is a schematic side sectionalview of the bonded semiconductor structure of FIG. 9A. The bondedstructure 100 of FIGS. 9A-9B can include a pair of bonded semiconductorelements 101. For ease of illustration, only one of the pair of bondedsemiconductor elements 101 is shown in FIG. 9A. The semiconductorelements 101 can comprise a wafer, a partially-processed wafer, and/or adiced or partially-diced semiconductor device, such as an integratedcircuit die or a microelectromechanical systems (MEMS) die. Eachsemiconductor element 101 can comprise a conductive contact structure102 and a non-metallic bonding region 106 proximate the contactstructure 102. As shown in FIGS. 9A-9B, for example, the bonding region106 can surround or be disposed about the contact structure 102. Theconductive contact structure 102 can comprise any suitable conductivematerial, including, e.g., a metal or a conductively-doped semiconductormaterial. For example, the contact structure 102 can comprise gold,copper, tungsten, nickel, silver, alloys thereof, or any other suitablematerial. The non-metallic bonding region 106 can comprise any suitablenonconductive material, including, e.g., a semiconductor material or aninsulating material (such as a polymer). For example, the bondingregions 106 can comprise at least one of silicon, silicon oxide, siliconnitride, glass, silicon-on-insulator, silicon carbide, sapphire,germanium, gallium arsenide, gallium nitride, polymers, indiumphosphide, or any other suitable non-metallic material.

The contact structure 102 includes contact features from each of theopposing or bonded pair of semiconductor elements 101. The contactstructure 102 of a first semiconductor element 101 can include a firstelongate contact feature 103 a, and the contact structure 102 of asecond semiconductor element (not shown in FIG. 9A) can comprise asecond elongate contact feature 103 b. In the embodiment of FIGS. 9A-9B,the first and second elongate contact features 103 a, 103 b can begenerally linear elements having a length larger than a width. Forexample, the length of the contact features 103 a, 103 b can be at leasttwice the width, at least five times the width, or at least ten timesthe width. Length is used to refer to the longer dimension of eachfeature in the bonding plane (e.g., the interfacial plane along whichthe two elements 101 are directly bonded) while width refers to thenarrower dimension in the bonding plane. Furthermore, it should beappreciated that elongate contact features may not be linear in otherembodiments. Rather, the elongate contact features may be curved, e.g.,such that the path length traversed by the contact feature in thebonding plane is longer than the width of the contact feature in thebonding plane.

The first elongate contact feature 103 a of the first semiconductorelement 101 can be disposed over and can be at least partially alignedwith an underlying interconnect 105, such as a through-silicon via(TSV). Internal metallization (not shown) may connect the interconnect105 with the contact structure 102 (e.g., first elongate contactstructure 103 a) of the first semiconductor element 101. For example,internal metallization or traces can be disposed laterally and/orvertically in the semiconductor element 101 to provide communicationbetween the interconnect 105 and the contact structures 102. Moreover,in some embodiments, a conductive barrier (not shown) can be providedbetween the contact structure 102 and the interconnect 105 orintervening internal metallization. For example, in some embodiments,the conductive barrier can line a trench of a damascene structure.Additional metallization may also be provided at or near the surface ofthe semiconductor elements 101 to route signals laterally across thewidth of the element. As shown in FIG. 9A, the interconnects 105 can bespaced apart by an interconnect pitch p and can serve to electricallyconnect the contact structures 102 to external leads which communicatewith the larger electronic system. The pitch p can be any suitabledistance, e.g., in a range of 0.1 microns to 500 microns, in a range of0.1 microns to 100 microns, in a range of 0.1 microns to 50 microns, ina range of 1 micron to 50 microns, or in a range of 10 microns to 50microns.

To bond the two semiconductor elements, as explained above, thesemiconductor elements 101 can be oriented relative to one another suchthat the first elongate contact feature 103 a of one of the opposingelements 101 is nonparallel with the second elongate contact feature 103b of the other of the opposing elements 101. The two semiconductorelements 101 can be brought together such that at least the first andsecond non-metallic bonding regions 106 are in contact. As explainedabove, the surfaces of the bonding regions 106 can be prepared suchthat, when the bonding regions 106 of two semiconductor elements 101 arebrought into contact, the non-metallic bonding regions 106 directly bondwith one another to form a chemical bond without an interveningadhesive. Thus, the portion of the non-metallic bonding region 106disposed on a first side of the first contact feature 103 a can bedirectly bonded with corresponding portions of the non-metallic bondingregion 106 disposed on both sides of the second contact feature 103 b.

For example, in various embodiments, the bonding regions 106 can bepolished and then very-slightly etched to create a smooth bondingsurface. In various embodiments, the etched surfaces can be terminatedwith a nitrogen-containing species by, for example, exposing the etchedsurfaces to a plasma comprising nitrogen (such as nitrogen gas) ordipping the etched surfaces in a nitrogen-containing solution (such asan ammonia-containing solution). In other embodiments, other terminatingspecies can facilitate the chemical, covalent bonding of thenon-metallic bonding regions 106 a, 106 b. In various embodiments, thebonding regions 106 can be directly bonded together at room temperature.The bonding regions 106 can also be directly bonded together withoutapplying external pressure to the semiconductor elements 101.

The first and second elongate contact features 103 a, 103 b canintersect one another at a contact intersection 104. As with theembodiments explained above with respect to FIGS. 1A-8C, the elongatecontact features 103 a, 103 b can be directly bonded to one another toprovide electrical communication between the features 103 a, 103 b. Forexample, in embodiments similar to those of FIGS. 1A-5C, where contactsprotrude, bonding of non-metal (e.g., semiconductor or insulator)surfaces between contacts creates internal pressure that can bond thecontact features 103 a, 103 b from opposing semiconductor elements, withor without the addition of heat. In embodiments similar to those ofFIGS. 8A-8C, after the bonding regions 106 have been directly bonded toone another, the semiconductor elements 101 can be heated to cause theelongate contact features 103 a, 103 b to expand toward one another dueto differential coefficient of thermal expansion (CTE) relative tosurrounding materials, generating the internal pressure that causes thefeatures 103 a, 103 b to be directly bonded to one another at theintersection 104. The semiconductor elements 101 can be heated in arange of 75° C. to 350° C., or more particularly, in a range of 100° C.to 250° C.

Advantageously, providing at least one elongate contact feature 103 aand/or 103 b can significantly increase the alignment tolerances fordirectly bonding conductive contact structures 102 together. Because atleast one of the contact features 103 a and/or 103 b is elongated with apath length longer than its width in the bonding plane, the twosemiconductor elements 101 can be misaligned by relatively large amountswhile still facilitating direct bonding between the contact features 103a, 103 b. For example, in bonded structures which utilize smaller ornon-elongated contact features, the alignment tolerance of conventionalpick-and-place machines may be in a range of 1 micron to 5 microns, orin a range of 1 micron to 10 microns.

By contrast, for an interconnect pitch p of 40 microns, the elongatecontact features 103 a, 103 b can have a length l of about 20 microns,or about half the pitch of the interconnect pitch p. Because the lengthl of each contact feature 103 a, 103 b is large relative to theinterconnect pitch p, it is easier for the pick-and-place machinery toachieve overlap or intersection between the two contact features 103 a,103 b, which results in a larger tolerance for misalignments. Forexample, in the example of a 40 micron interconnect pitch, themisalignment tolerance (i.e., the degree to which the semiconductorelements 101 may be misaligned relative to one another laterally) can bein a range of 5 microns to 10 microns.

It should be appreciated that, in other embodiments, other suitablelengths l may be used. For example, the length l of the elongate contactfeatures 103 a, 103 b shown in FIGS. 9A-9B may be in a range of 0.05microns to 500 microns, in a range of 0.05 microns to 100 microns, in arange of 0.05 microns to 50 microns, in a range of 0.1 microns to 50microns, in a range of 1 micron to 50 microns, in a range of 5 micronsto 50 microns, in a range of 10 microns to 50 microns, in a range of 10microns to 40 microns, or in a range of 15 microns to 30 microns. Thewidth of the contact features 103 a, 103 b can be sufficiently small soas to reduce parasitic capacitance and to maintain a small footprint onthe semiconductor elements 101. For example, the width of the contactfeatures 103 a can be in a range of 0.01 microns to 10 microns, in arange of 0.01 microns to 5 microns, in a range of 0.1 microns to 10microns, in a range of 0.1 microns to 5 microns, in a range of 0.5microns to 5 microns, 0.5 microns to 4 microns, in a range of 1 micronto 5 microns, in a range of 1 micron to 3.5 microns, or in a range of1.5 microns to 3 microns.

Although both contact features 103 a, 103 b shown in FIGS. 9A-9B areillustrated and described as linear contact features, it should beappreciated that in other embodiments, the elongate contact features caninstead comprise curved shapes. For example, it should be appreciatedthat the first semiconductor element can comprise a curved contactfeature, and the second semiconductor element can comprise any one of alinear contact feature, a two-dimensionally patterned contact feature(e.g., a grid contact feature), a curved contact feature, etc. Thus,misalignment can be reduced while still minimizing dishing (andconsequent uniformity problems for the height/depth of contacts) so longas the path length (e.g., whether a linear path length or a curved pathlength) is sufficiently longer than the width of the contact feature.Additional elongate contact features are illustrated below in connectionwith FIGS. 12A-12H.

The contact features 103 a, 103 b can comprise protruded contactsextending above the bonding regions 106. For example, the contactfeatures 103 a, 103 b can comprise protruded contacts similar to themetallic pads 12, 15 shown in the embodiment of FIGS. 1A-1D. In otherembodiments, the contact features 103 a, 103 b can comprise recessedcontacts in which the contact features 103 a, 103 b are initiallydisposed below the bonding regions 106 and are brought into contactafter the bonding regions 106 are directly bonded together (e.g.,similar to that shown in FIGS. 6A-6C and 8A-8C). In still otherembodiments, one of the contact feature 103 a or 103 b can comprise aprotruded contact, and the other of contact feature 103 a, 103 b cancomprise a recessed contact (e.g., similar to that shown in FIGS.7A-7C).

FIG. 10 is a schematic top plan view of a bonded semiconductor structure100, according to another embodiment. Unless otherwise noted, referencenumerals shown in FIG. 10 represent components generally similar tothose referenced in FIGS. 9A-9B. For example, each of two bondedsemiconductor elements 101 can include corresponding conductive contactstructures 102 and non-metallic bonding regions 106 disposed proximatethe contact structures 102. The conductive contact structures 102 cancomprise elongate contact features 103 a, 103 b. Unlike the embodimentof FIGS. 9A-9B, however, in the embodiment of FIG. 10, the contactfeatures 103 a, 103 b can comprise a two-dimensionally patterned contactfeature, e.g., plurality of intersecting conductive segments that definea two-dimensional pattern of elongate contact features for improvingalignment in bonded structures. The intersecting conductive segments canbe curved, linear, polygonal, circular, elliptical, etc. For example, inFIG. 10, corresponding orthogonal grid patterns can be disposed on thesemiconductor elements 101. By contrast, FIGS. 12A-12H illustrateadditional embodiments in which patterns of elongate contact features103 a, 103 b may define other two-dimensional shapes that may assist inimproving rotational alignment of bonded structures.

The grid patterns of the contact features 103 a, 103 b of FIG. 10 cancomprise multiple intersecting lines. Although the intersecting lines ofthe grid patterns of FIG. 10 are shown as being perpendicular to oneanother, in other embodiments, the intersection lines of the gridpatterns can instead be disposed at non-perpendicular angles.Furthermore, although each of the multiple lines of the grid patternsare linear in FIG. 10, in other embodiments, the lines of the gridpattern can instead be curved. See, for example, the patterns of FIGS.12A-12H.

The length l of the grid pattern can have the same lengths l as thelines of the embodiment of FIGS. 9A-9B. For example, the length l of thegrid pattern can be in a range of 0.05 microns to 500 microns, in arange of 0.05 microns to 100 microns, in a range of 0.05 microns to 50microns, in a range of 0.1 microns to 50 microns, in a range of 1 micronto 50 microns, in a range of 5 microns to 50 microns, in a range of 10microns to 50 microns., in a range of 10 microns to 40 microns, or in arange of 15 microns to 30 microns. The width of each of the lines of thegrid pattern of the contact features 103 a, 103 b can be sufficientlysmall so as to avoid dishing issues that may interfere with reliablemetal bonding across semiconductor elements 101. For example, the widthof the multiple lines of the grid pattern of the contact features 103 acan be in a range of 0.01 microns to 10 microns, in a range of 0.01microns to 5 microns, in a range of 0.1 microns to 10 microns, in arange of 0.1 microns to 5 microns, in a range of 0.5 microns to 5microns, 0.5 microns to 4 microns, in a range of 1 micron to 5 microns,in a range of 1 micron to 3.5 microns, or in a range of 1.5 microns to 3microns. The separation distance d between adjacent lines of the gridpattern can be any suitable distance, e.g., in a range of 0.01 micronsto 100 microns, 0.01 microns to 50 microns, in a range of 0.1 microns to50 microns, in a range of 0.5 microns to 50 microns, in a range of 0.5microns to 10 microns, in a range of 0.5 microns to 5 microns, or in arange of 1 micron to 5 microns.

Advantageously, the use of grid patterns as the contact features 103 a,103 b can enable for an intersecting region 104 that has multipleelectrical, direct bonded contacts. Because the grid pattern comprisesmultiple intersecting lines, the embodiment of FIG. 10 may enable thecreation of electrical contacts while accommodating large amounts ofmisalignment. Furthermore, as compared with the embodiment of FIGS.9A-9B, the creation of multiple electrical connections within a gridpattern can allow a lower current density, at least because there is agreater contact area. For example, in the embodiment of FIG. 10, thetotal surface area of the contact (i.e., the area in which the contactfeatures 103 a, 103 b are directly bonded) can be in a range of 10 μm²to 30 μm², or in a range of 5 μm² to 35 μm², or, more particularly, in arange of 10 μm² to 25 μm². The current for each contact is spread over agreater number of connections with higher overall contact surface, thusreducing the current density for a given current.

The grid pattern shown in FIG. 10 comprises an m×n array of cells, inwhich m=n=4. It should be appreciated, however, that the grid patterncan comprise any number of cells, and m, n can be even or odd. Forexample, in an alternative grid pattern, the m×n array of cells cancomprise an odd number of cells, e.g., m=n=1, 3, 5, etc. In suchembodiments, the use of an odd number of cells may enable a constantcrossover area at a given misalignment for a minimum contact structurearea (for example, when the extent of each cell is comparable to thealignment accuracy). The lines of the grid pattern can be narrower thanthe spacing between the grid lines to help reduce dishing and increasebond energy of the non-metallic portions. The size or extent of the cellthat can be repeated to comprise the grid can be comparable to the 3sigma alignment accuracy of the alignment tool(s) used to align andplace bonding surfaces together such that at least two connection pointshave an area given by the product of line widths on the opposed bondingsurfaces when m=1. The number of connection points can then increasewhen m=1. The interconnection area can be increased by increasing thenumber of connection points or increasing the width of the line in thegrid.

In conventional bonding arrangements, a separate metallic layer (e.g.,an aluminum pad) may be created near the top surface of thesemiconductor element so as to enable electrical communication betweentwo bonded semiconductor elements 101 a, 101 b. Moreover, the metalliccontact pad may be relatively large so as to accommodate thecorresponding contacts or bumps on the opposing semiconductor element,which can increase parasitic capacitance. In such conventionalarrangements, vertical connections, such as vias or TSVs extend from thecontact pads into the semiconductor element(s) to connect withcorresponding traces for signal routing. In such arrangements,therefore, the contact pads are relatively large, and multiple tracelayers may be used to ensure that the signals are routed properly. Thevertical connections occupy layers that could otherwise be employed forlateral routing.

FIGS. 11A-11C illustrate the use of elongate contact features 103 a, 103b to provide electrical communication with corresponding underlyingtraces 120 for the reliable routing of electrical signals through thesemiconductor elements 101 a, 101 b. In particular, FIG. 11A is aschematic top plan view of a first semiconductor element 101 a having aplurality of elongate contact features 103 a connected withcorresponding underlying traces 120 a. FIG. 11B is a schematic top planview of an exemplary contact feature 103 a and associated underlyingtraces 120 a of the first semiconductor element 101 a, and also shows acontact feature of a second semiconductor element aligned to makecontact in a crossing orientation with a contact feature of the firstsemiconductor element. FIG. 11C is a schematic side cross-sectional viewof two bonded semiconductor elements 101 a, 101 b including a directconnection between crossing contact features 103 a, 103 b of eachelement 101 a, 101 b.

As shown in FIG. 11A, the first semiconductor element 101 a can includea plurality of contact structures 102 comprising elongate contactfeatures 103 a exposed at a top surface of the first semiconductorelement 101 a. As with the embodiments of FIGS. 8A-10, a non-metallicbonding region 106 can be disposed proximate or surrounding the contactfeatures 103 a, and the non-metallic bonding region 106 can cover thetraces 120 a. Each contact feature 103 a is electrically connected withand preferably extends from a corresponding trace 120 a which isdisposed below the contact feature 103 a. Thus, the traces 120 a shownin FIG. 11A are embedded within the semiconductor element 101 a belowthe contact features 103 a. The traces 120 a can be jogged or offsetrelative to one another so as to enable the reliable routing of traces120 a for each contact feature 103 a without crosstalk. While FIG. 11Ashows the contact features 103 a as wider than the underlying traces 120a for purposes of illustration, it will be understood from FIGS. 11B and11C below that in fact the contact features can have the same width asthe underlying traces 120 a. For example, in some arrangements, thewidth of the trace 120 a and the width of the contact feature 103 a canbe in a range of 0.5 micron to 5 microns, in a range of 1 micron to 3microns, e.g., about 2 microns.

As shown in FIGS. 11B-11C, the exemplary contact feature 103 a can bedisposed on top of the corresponding trace 120 a to which the exemplarycontact feature 103 a is connected. The elongate contact feature 103 acan extend along only a portion of the trace 120 a and can have a length1 and a width w selected so as to ensure that the contact feature 103 aof the first semiconductor element 101 a intersects and contacts acorresponding contact feature 103 b of the second semiconductor element101 b. The contact feature 103 b of the second semiconductor element 101b is shown in FIG. 11B for purposes of illustrating their relativeorientations when aligned for contact.

The length l of the elongate contact features 103 a, 103 b shown inFIGS. 11a-11c may be in a range of 0.05 microns to 500 microns, in arange of 0.05 microns to 100 microns, in a range of 0.05 microns to 50microns, in a range of 0.1 microns to 50 microns, in a range of 1 micronto 50 microns, in a range of 5 microns to 50 microns, in a range of 10microns to 50 microns, in a range of 10 microns to 40 microns, or in arange of 15 microns to 30 microns. The width w of the contact features103 a, 103 b can be sufficiently small so as to avoid dishing problems,reduce parasitic capacitance and to maintain a small footprint on thesemiconductor elements 101. For example, the width of the contactfeatures 103 a can be in a range of 0.01 microns to 10 microns, in arange of 0.01 microns to 5 microns, in a range of 0.1 microns to 10microns, in a range of 0.1 microns to 5 microns, in a range of 0.5microns to 5 microns, 0.5 microns to 4 microns, in a range of 1 micronto 5 microns, in a range of 1 micron to 3.5 microns, or in a range of1.5 microns to 3 microns. The width 2 of the contact features may be thesame, or within ±10%, more particularly within ±5%, of the widths of thetraces 102 a from which they extend.

As shown in FIG. 11C, the contact feature 103 a from the firstsemiconductor element 101 a can contact and be bonded to thecorresponding contact feature 103 b from the second semiconductorelement 101 b at an intersection region 104. The exemplary contactfeature 103 a shown in FIG. 11C can be disposed over and in electricalcontact with only the trace 120 a associated with that contact feature103 a. Within the same metallization level, traces 120 a associated withother contact features (not shown) can extend generally parallel withand not intersect the trace 120 a associated with the illustratedcontact feature 103 a. Similarly, the exemplary contact feature 103 b ofthe second semiconductor element 101 b can extend over and be inelectrical contact with only the trace 120 b associated with thatcontact feature 103 b. As shown in FIG. 11C, the contact feature 103 band its trace 120 b can extend non-parallel (e.g., generallyperpendicular) relative to the contact feature 103 a and its trace 120a. Although the trace 120 b is illustrated in FIG. 11C as extendinglaterally (e.g., non-parallel with the traces 120 a), in otherarrangements, the contact feature 103 b of the second element 101 b canbe connected with other types of internal routing features, includingvertical and/or horizontal routing features, or routing features thatextend in any other direction. Furthermore, in some arrangements, therouting features for the first semiconductor element 101 a may bedifferent from the routing features of the second semiconductor element101 b. For example, the traces 120 a may only be formed in the firstelement 101 a, and other types of routing features may be formed in thesecond element 101 b.

Advantageously, the embodiment illustrated in FIGS. 11A-11C can enablethe use of smaller contact features which can reduce parasiticcapacitance while improvement the alignment accuracy of the bondedstructures. Moreover, the positioning of the contact features 103 a, 103b relative to the corresponding traces 120 a, 120 b can enable efficientrouting of electrical signals without providing multiple routing and/orcontact layers. As the illustrated contact features 103 a extenddirectly from underlying lateral traces, the metallization level isfully employed for lateral routing without the need for interveninginterlevel dielectrics (ILDs) solely for vertical connections (such asvias). As with the embodiments of FIGS. 9A-10, the semiconductorelements 101 a, 101 b can comprise any suitable type of semiconductorelement. For example, in one embodiment, the first semiconductor element101 a may comprise an interposer and the second semiconductor element101 b may comprise an integrated device die. In other embodiments, bothsemiconductor elements 101 a, 101 b may comprise integrated device dies.

FIGS. 12A-12H are schematic top plan views of conductive contactstructure 102, according to various other embodiments. Unless otherwisenoted, reference numerals shown in FIGS. 12A-12H represent componentsgenerally similar to those referenced in FIGS. 8A-11C. For example, asemiconductor element (not shown) can include corresponding conductivecontact structures 102 and non-metallic bonding regions 106 disposedproximate the contact structures 102. The conductive contact structures102 can comprise elongate contact features 103 a, 103 b. In FIGS.12A-12H, only one contact feature 103 a, associated with a correspondingsemiconductor element, is shown. As with the embodiment of FIG. 10, thecontact features 103 a, 103 b can comprise a two-dimensionally patternedcontact feature, e.g., a plurality of intersecting conductive segmentsthat define a two-dimensional pattern of elongate contact features forimproving alignment in bonded structures. For example, the contactfeatures 103 a of FIGS. 12A-12H can comprise bounded structures ofelongate segments disposed about a central region. The contact features103 a shown in FIGS. 12A-12H define patterns of elongate contactfeatures that may assist in improving rotational alignment of bondedstructures. For example, in FIGS. 12A-12H, the contact structures 102may comprise rotationally symmetric, or near symmetric, elongate contactfeatures 103 a. Thus, the elongate contact features 103 a of FIGS.12A-12H can accommodate for linear misalignment, since the contactstructure 102 includes a plurality of elongate conductive segments. Theelongate contact features 103 a can also accommodate for rotationalmisalignments, because outwardly-extending segments 122 of tworotationally-misaligned contact structures 102 may provide sufficientelectrical connection between two bonded semiconductor elements.

The pattern of the contact structure 102 may comprise any suitableshape. For example, as shown in FIG. 12A, the contact structure 102 cancomprise a polygonal boundary B (e.g., a quadrilateral, rectangular orsquare boundary) disposed about a central region C, which may or may notbe at the geometric center of the contact structure 102. Theoutwardly-extending segments 122 can extend radially outward from thecentral region C, so as to reduce rotational and lateral misalignments.As with FIG. 12A, the contact structure 102 of FIG. 12B can comprise apolygonal boundary B disposed about the central region C. In addition, aplurality of lateral connectors 124 can interconnect theoutwardly-extending segments 122, which may further reducemisalignments.

FIGS. 12C-12D illustrate contact structures 102 having a polygonalboundary B, which comprises a pentagonal boundary. In FIG. 12D, thelateral connectors 124 can interconnect the outwardly-extending segments120. FIGS. 12E-12F illustrate contact structures 102 having a polygonalboundary B, which comprises a hexagonal boundary. In FIG. 12F, thelateral connectors 124 can interconnect the outwardly-extending segments120. Although FIGS. 12A-12F depict polygonal boundaries ofquadrilateral, pentagonal, and hexagonal profiles, it should beappreciated that any suitable polygonal boundary may be used. Moreover,as shown in FIGS. 12G-12H, the contact structures 102 may also comprisecurved contact features 103 a, e.g., circular or elliptical boundariesB. FIG. 12H illustrates lateral connectors 124 connecting theoutwardly-extending segments 120.

Thus, the elongate contact features 103 a, 103 b disclosed herein candefine any suitable pattern. Beneficially, the contact features 103 a,103 b can improve lateral and/or rotational misalignments, whileproviding electrical interconnection between directly bondedsemiconductor elements.

Numerous modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

What is claimed is:
 1. A bonded structure comprising: a firstsemiconductor element comprising a conductive first contact structureand a non-metallic first bonding region proximate the first contactstructure, the first contact structure comprising a conductive firstelongate contact feature; and a second semiconductor element comprisinga conductive second contact structure and a non-metallic second bondingregion proximate the second contact structure, the second contactstructure comprising a conductive second contact feature, wherein thefirst bonding region is in contact with and directly bonded to thesecond bonding region, and wherein the first elongate contact feature isoriented non-parallel with and directly contacts the second contactfeature at an intersection between the first elongate contact featureand the second contact feature.
 2. The bonded structure of claim 1,wherein the first elongate contact feature is directly bonded with thesecond contact feature at the intersection.
 3. The bonded structure ofclaim 1, wherein the second contact feature comprises an elongatecontact feature.
 4. The bonded structure of claim 3, wherein an oxide ona first side of the first elongate contact feature is bonded withcorresponding oxide regions on first and second sides of the secondelongate contact feature.
 5. The bonded structure of claim 1, whereinthe first contact structure comprises a plurality of lines in a gridpattern.
 6. The bonded structure of claim 1, wherein the first contactstructure defines a boundary disposed about a central region and aplurality of conductive segments extending outwardly from the centralregion.
 7. The bonded structure of claim 6, further comprising aplurality of lateral connectors that connect the plurality of conductivesegments.
 8. The bonded structure of claim 7, wherein the boundarycomprises a polygonal or rounded pattern.
 9. The bonded structure ofclaim 1, wherein the first elongate contact feature has a length and awidth, the length being at least twice the width.
 10. The bondedstructure of claim 9, wherein the length of the first elongate contactfeature is at least five times the width.
 11. The bonded structure ofclaim 1, wherein at least one of the first and second contact structurescomprises at least one of a metal and a conductively-doped semiconductormaterial.
 12. The bonded structure of claim 1, further comprising athrough-silicon via (TSV) disposed within the first semiconductorelement below the intersection of the first elongate contact feature andthe second contact feature.
 13. The bonded structure of claim 12,further comprising one or more conductive traces disposed between andelectrically connecting the TSV with the first elongate contact feature.14. The bonded structure of claim 1, wherein at least one of the firstelongate contact feature and the second contact feature is curved.
 15. Abonding method comprising: providing a first semiconductor elementcomprising a conductive first contact structure and a non-metallic firstbonding region proximate the first contact structure, the first contactstructure comprising a conductive first elongate contact feature;providing a second semiconductor element comprising a conductive secondcontact structure and a non-metallic second bonding region proximate thesecond contact structure, the second contact structure comprising aconductive second contact feature; orienting and bringing together thefirst and second semiconductor elements, such that the first elongatecontact feature and the second contact feature are nonparallel; directlybonding the first bonding region with the second bonding region; anddirectly bonding the first elongate contact feature and the secondcontact feature at an intersection between the first elongate contactfeature and the second contact feature.
 16. The method of claim 15,wherein directly bonding the first bonding region with the secondbonding region comprises leaving an initial gap between the firstelongate contact and the second contact feature, and heating the firstand second semiconductor elements to cause the first elongate contactfeature to directly contact the second elongate contact feature.
 17. Themethod of claim 15, further comprising, before directly contacting,forming the first elongate contact feature directly on a correspondingtrace, the trace aligned along a length of the first elongate contactfeature.
 18. A semiconductor element comprising: a substrate comprisingone or more layers of non-metallic material; a plurality of conductivetraces embedded in the substrate, the traces extending laterally throughthe substrate to route electrical signals laterally; and an elongatecontact feature extending along and directly contacting a first trace ofthe plurality of traces, the contact feature exposed at a top surface ofthe substrate.
 19. The semiconductor element of claim 18, wherein thecontact feature extends along a portion of a length of the first trace.20. The semiconductor element of claim 18, wherein the elongate contactfeature covers a first portion of the first trace, and wherein aninsulating material covers a second portion of the first trace.